4.1 Case Insensitive Comparisons

When a standard utility or function that uses regular expressions or pattern matching specifies that matching shall be case insensitive, then if a string would match the regular expression or pattern when doing a case-sensitive match, the same string with any of its characters replaced with their case counterparts, as defined by the toupper and tolower character mappings (see [xref to XBD 7.3.1]), shall also match when doing a case-insensitive match.

This definition of case-insensitive processing is intended to allow matching of multi-character collating elements as well as characters, as each character in the string is matched using both its cases. For example, in a locale with a "Ch" multi-character collating element (see [xref to XBD 7.3.2 bullet 1]), the bracket expression <tt>"[[.Ch.]]"</tt> (see [xref to XBD 9.3.5 bullet 4]) matches the strings <tt>"ch"</tt>, <tt>"Ch"</tt>, <tt>"cH"</tt>, and <tt>"CH"</tt> when matching without regard to case.

When a standard utility or function that uses regular expressions specifies that pattern matching shall be performed without regard to the case (uppercase or lowercase) of either data or patterns, then when each character in the string is matched against the pattern, not only the character, but also its case counterpart (if any), shall be matched. This definition of case-insensitive processing is intended to allow matching of multi-character collating elements as well as characters, as each character in the string is matched using both its cases. For example, in a locale where "Ch" is a multi-character collating element and where a matching list expression matches such elements, the RE "<tt>[[.Ch.]]</tt>" when matched against the string "<tt>char</tt>" is in reality matched against "<tt>ch</tt>", "<tt>Ch</tt>", "<tt>cH</tt>", and "<tt>CH</tt>".

Some standard utilities and functions support case-insensitive regular expression matching. When this type of matching is in effect, the matching process shall be modified as described in [xref to XBD 4.1].

-iname pattern

The -iname primary shall be equivalent to -name, except that the match shall be case insensitive. See [xref to XBD 4.1].

used in the pattern matching notation for the -n option

used in the pattern matching notation for the -name, -iname and -path primaries

within the pattern matching notation used for the -n option

within the pattern matching notation used for the -name, -iname and -path primaries

Perform pattern matching in searches without regard to case;

Perform pattern matching in a case-insensitive manner;

Perform pattern matching in searches without regard to case;

Perform pattern matching in a case-insensitive manner;

FNM_CASEFOLD string and pattern are compared in a case-insensitive manner. See [xref to XBD 4.1].

FNM_IGNORECASE Equivalent to FNM_CASEFOLD.

Ignore case in match

Perform pattern matching in a case-insensitive manner

If FNM_CASEFOLD or FNM_IGNORECASE is set, string and pattern shall be compared in a case-insensitive manner. See [xref to XBD 4.1].

Ignore case in match (see [xref to XBD Chapter 9])

Perform matching in a case-insensitive manner (see [xref to XBD 9.2])

A.4.1 Case Insensitive Comparisons

Case-insensitive matching is defined in this standard in terms of a simple algorithm whereby, for each character in the string to be matched, if the character is uppercase then the lowercase equivalent (if any) is also checked for a match, and if the character is lowercase then the uppercase equivalent (if any) is also checked for a match. It is described this way to make the expected behavior easier to understand; however, implementations may internally use more sophisticated algorithms to improve efficiency, provided that the result is the same as the simple algorithm would produce.